What makes aluminium chloride covalent whilst aluminium oxide is ionic?

Aluminium chloride forms covalent bonds because it is composed of a metal (aluminium) and a non-metal (chlorine), leading to sharing of electrons. Aluminium oxide is ionic because it is composed of a metal (aluminium) and a non-metal (oxygen), resulting in the transfer of electrons from the metal to the non-metal, creating positively and negatively charged ions that are held together by electrostatic forces.